So I managed to break the screen on my iMac. Yeah, I know...I bought a replacement off eBay but it seems to be faulty. I thought there might be a problem as soon as I started the Sierra installer - highlighted buttons had a bright blue line round them. The screen displays as normal but then it flickers and goes a weird blue colour, then back to normal. My gut tells me the screen unit is faulty, but just in case, is anyone reading this thinking "I know what that is and isn't faulty"?Worst of it is - it's only the glass that is cracked on the old screen but it seems that the only way to repair it is to replace the entire screen unit.